Two solid rubber balls A and B  having masses 200 and 400 gm respectively are moving in opposite directions with velocity of A equal to 0.3 m/s. After collision the two balls come to rest, then the velocity of B is

Initial linear momentum of system =  mAv→A+mBv→B                                        = 0.2 × 0.3 + 0.4 × vBFinally both balls come to rest ∴ final linear momentum = 0 By the law of conservation of linear momentum       0.2 × 0.3 + 0.4 × vB = 0∴vB=−0.2×0.30.4=−0.15 m​/​s